1. Field of the Invention
The present invention relates to a lithium secondary battery, and more particularly, to a lithium secondary battery having excellent storage characteristics at a high temperature and excellent lifetime characteristics.
2. Description of Related Art
As the electronic, communication, and computer industries are rapidly developed, portable electronic communication devices such as camcorders, cellphones, notebook PCs, and/or the like are dramatically improved. Thus, demand for lithium second batteries as power sources to drive the above devices is increased daily. In particular, related to eco-friendly power sources of applications such as electronic vehicles, uninterruptible power devices, power tools, satellites, and/or the like, research and development are being actively progressed in Japan, Europe, the United States of America, and/or the like as well as in Korea.
Lithium secondary batteries developed in the early 1990s among currently applied secondly batteries are composed of a negative electrode formed of a carbon material, etc., which is capable of adsorbing and ejecting lithium ions, a positive electrode formed of lithium based oxides, etc., and a non-aqueous electrolyte in which lithium salts are dissolved in a composite organic solvent by a proper amount.
However, as application ranges of the lithium secondary batteries are increased, cases for using the lithium secondary batteries under more harsh environmental conditions, such as a high temperature or low temperature condition, are increased.
However, metal components of lithium transition metal oxides or the complex oxides which are used as positive active materials of the lithium secondary batteries are separated from the positive electrode in a fully charged state during high temperature storage, and thus become thermally unstable.
In order to solve the above problem, Korean Patent Publication No. 10-2006-0134631 disclosed core-shell structured positive active materials with high capacity and safety and their preparing method for lithium secondary batteries, but the lifetime characteristics are not increased sufficiently.